This invention pertains to the art of cooking appliances and, more particularly, to a speed cooking oven that utilizes slotted antenna for efficient distribution of microwave energy to a food product within the cooking chamber of the speed cooking oven. The invention has particular application to high speed cooking of food products at very high quality standards.
As used herein the terms “conventional cooking oven”, “conventional cooking” and “conventional means”, have the same meaning and refer to cooking at the quality level and at the speed that is currently widely utilized.
An important aspect of proper speed cooking is that the food product produced in a speed cook oven (in one seventh to one tenth the time of a conventional oven) is at or above the taste, appearance, quality and performance levels of the same food product cooked by conventional means.
Fast cooking ovens in the 2 to 3 times speed range have also been developed but are limited by inefficiencies. The first limitation is that the microwave launch system cannot equally illuminate multiple racks or pans of food. As a result, the efficiency of the microwave energy system must be purposely reduced (limited) in order to avoid hot spots and poor cooking quality. Second, in a top (roof) launch or bottom (floor) launch microwave system, cooking pans or other cooking vessels containing the food are situated directly above (in a bottom launch system) or directly below (in a top launch system) the microwave launch system. This obscures the microwave energy from the pans further away from the microwave illumination source. To compensate for the non-uniform illumination of the microwaves within the oven cavity, the design of the microwave system is purposely limited in order to achieve uniformity. As a result, most traditional microwave convection ovens are actually single rack ovens. Many of these top or bottom launch systems require either a mechanical device (generally referred to as a mode stirrer) or a turntable that rotates a platter or plate upon which the food rests (in a top launch microwave system), or in some cases both a mode stirrer and a rotating tray is utilized, to stir the electromagnetic energy field (“e-field”) produced by the magnetrons. As used herein the terms “microwave energy”, “electromagnetic energy”, “e-field” and “e-fields” all have the same meaning.
A disadvantage of bottom launch microwave systems is that it is difficult to provide a microwave seal to the cavity floor (microwave energy launching through the oven floor via a circular waveguide) to prevent grease and liquid contamination of the waveguide chamber. A waveguide launcher sealing material must be utilized that allows for the passage of the e-field through the sealing material without any leakage of the seal. This is important because grease, water vapor or other particulate contamination of the microwave waveguide causes premature failure of the magnetron used to generate the e-field within the waveguide. Some speed cook ovens use an impingement approach where vertical air jets are generated from the oven cavity roof and floor simultaneously. The oven cavity bottom air jets (floor impingement jets) provide for bottom side cooking and browning while the oven cavity roof jets provide top side cooking and browning. In these devices, the e-field is launched from above the food product but this approach has disadvantages because the general oven construction is complex and the supply duct to the roof air plate must also act as a waveguide launcher for the e-fields. As used herein the terms “microwave waveguide”, “waveguide”, “waveguide launcher”, “guide” and “launcher” have the same meaning. This requires that the roof jet plate be transparent to the e-field (e.g., ceramic plate with jet impingement holes) so that the e-field can be launched through the ceramic plate. Additionally, the floor ducts may become complex parts to manufacture in the event they are designed to be removed for cleaning and/or servicing.
Generally, metal cooking devices such as cooking pans, cookie sheets and other metal cookware are traditionally used in conventional cooking. Because e-fields cannot penetrate these metal devices, all of the microwave energy must enter the top and side surfaces of the food product and speed cooking is therefore slowed by the use of metal pans because e-fields cannot penetrate the metal pans but are instead deflected (redistributed) within the oven cavity by the metal pans. To overcome this disadvantage, some ovens utilize a top launch microwave system. The theory has been to provide microwave energy through the top surface of the food product, but this application of microwave energy applies excessive microwave energy to the top of the product, causing over cooking, producing a tough, rubbery food product. The overcooking problem is especially acute when cooking proteins, such as meat. In order to prevent this microwave overcook condition, one method historically utilized has been to reduce the microwave energy that is available for cooking the food product. The result of limiting the microwave energy to the food product is that the microwave energy is more evenly distributed over the cook cavity, but this reduction in applied microwave energy results in a slower cooking process, defeating the desire for a speed cooking oven.
Other methods of distributing microwave energy launch e-fields from below the food product. This is not optimum because microwave energy that is to enter the upper surface of the food product must bounce around within the oven cook cavity in a random and inefficient manner in order to enter the top side of the food.
Accordingly, it is an object of the present invention to provide efficient electromagnetic distribution for speed-cooking within single-rack and multiple rack ovens capable of cooking most food products 5 to 10 times faster than conventional cooking.
A further object is to provide such a speed-cooking oven with a continuous floor that is not interrupted by microwave launching systems and is easy for the user to clean and maintain.
Still another objects is to provide a speed cooking oven that is capable of high quality speed cooking within metal pans, pots, sheet pans and other metal cooking devices commonly found in residential and commercial kitchens.
It is a further object to provide such an oven with a microwave distribution system which is more cost effective to manufacture and easier to clean and maintain.
Yet another object is to provide such a microwave distribution system which is more reliable due to improvements and simplifications.
Another object is to provide such a microwave distribution system that eliminates line of sight slot antenna interference.
Other objectives, features and advantages will be apparent in the written description which follows.